1. Field of the Invention
The present invention is directed to a manganese-nickel mixed hydroxide for battery active material and a process for the manufacturing thereof.
2. Description of the Related Art
Under circumstances that need to provide high energy density to batteries is required more and more, a nickel hydroxide positive electrode, which is commonly used for an alkaline storage battery, such as a nickel-cadmium storage battery and a nickel-metal hydride storage battery, is shifting from the sintered type to the paste type, which can provide high capacity and density to a battery. The paste-type nickel positive electrode has been produced by filling up nickel hydroxide powder together with an other metal powder, such as cobalt, into either a foam nickel plate or a nickel fiber plate, having a high porosity as much as 95%, and then pressing and molding the plate. Such foam nickel plates are obtained by plating a foam plastic, such as urethane, with nickel, and then heating and subjecting the plated plastic to thermal degradation.
In general, the reaction of nickel hydroxide as a positive electrode material for alkaline storage batteries during charging and discharging utilizes a reaction resulting in between .beta.-Ni(OH)2 and .beta.-NiOOH. This reaction is one electron reaction, however, this is the most stable reaction and it has therefore been commonly used.
When the reaction is changed to a multi electron reaction by utilizing a reaction which results in between .beta.-Ni(OH)2 and .gamma.-NiOOH, it is advantageous in increasing the capacity of batteries. However, in this case, there is a problem in the discharge reaction such that the discharge reaction being caused from .gamma.-NiOOH, which is generated at charging and discharging, to .beta.-Ni(OH)2 becomes difficult due to the difference in the lattice constants of .beta.-Ni(OH)2 and .gamma.-NiOOH.
There is also an advantage in increasing the capacity of batteries when the reaction between a .alpha.-Ni(OH)2 and .gamma.-NiOOH is utilized, as it is also an multi-electrons reaction. Furthermore, because of less difference in the lattice constants between .alpha.-Ni(OH)2 and .gamma.-NiOOH, it is more preferable to utilize this reaction as it allows a reduction in the change in the volume at charging and discharging.
However, it has been practically not feasible to utilize this reaction due to the fact that .alpha.-Ni(OH)2 is unstable in an alkaline solution and it easily changes to .beta.-Ni(OH)2.
For solving such problems as described above, it is an object of the present invention to provide a nickel hydroxide active material, which provides excellent discharging property and allows in particular to improve a discharge utilization, when such active material is used as an electrode material for batteries, and a process for the manufacture thereof.